1. Field of the Invention
The present invention generally relates to memory devices, and more particularly, the present invention relates to phase-change memory devices and to methods of fabricating the same.
A claim of priority is made to Korean Patent Application No. 10-2005-0098191 filed on Oct. 18, 2005 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety.
2. Description of the Related Art
Phase-change random access memories (PRAMs) store data using a phase-change material, e.g., a chalcogenide alloy, which is responsive to temperature to be selectively programmed into a crystalline state or an amorphous state. The resistance of a crystalline phase-change material is relatively low when compared to an amorphous phase-change material is high. In conventional nomenclature, the crystalline state is referred to as a “set” state or “0” state, and the amorphous state is referred to as a “reset” state or “1” state.
A phase-change memory device includes a plurality of memory cells located at intersections of a plurality of bit lines and a plurality of word lines. Each phase-change memory cell has a phase-change material whose resistance varies depending on current flowing through it and an access device (e.g., a cell diode) which controls the current flowing through the phase-change material. The current causes temperature variations in the phase-change material to thereby program the memory cell in the set or reset states.
It is desirable that the phase-change material have a high endurance characteristic in which it maintains its phase-change properties even after being subjected to repeated read and/or write operations. In a conventional phase-change memory device, the phase-change material is independently formed for each phase-change memory cell by etching. However, the phase-change material is susceptible to defects since it is highly sensitive to etching. Any such defects can adversely impact the endurance of the phase-change material.
In addition, design rules have been reduced in an effort to manufacture large-capacity, highly integrated phase-change memory devices. However, processing complexities make it difficult to independently fabricate a phase-change material for each phase-change memory cell, particularly in highly integrated phase-change memory devices.